Mental calculation increases physiological postural tremor, but does not influence physiological goal-directed kinetic tremor

Abstract

Purpose During a cognitive effort, an increase in cortical electrical activity, functional alterations in the anterior cingulate cortex, and modifications in cortical inputs to the active motor units have been reported. In light of this, an increase in tremor could be anticipated as result of a mental task. In the present work, we tested this hypothesis. Methods In 25 individuals, tremor was measured with a three-axial accelerometer during 300 s of postural and goal-directed tasks performed simultaneously to mental calculation, or during control (same tasks without mental calculation). Hand and finger dexterity were also evaluated. Electromyographic (EMG) recordings from the extensor digitorum communis were collected during the postural task. Results Hand and finger dexterity was negatively affected by the mental task (p = .003 and p = .00005 respectively). During mental calculation, muscle tremor increased in the hand postural (+ 29%, p = .00005) but not in the goal-directed task (− 1.5%, p > .05). The amplitude of the main frequency peak also increased exclusively in the hand postural task (p = .028), whilst no shift in the position of the main frequency peak was observed. EMG was not affected. Conclusion These results support the position of the contribution of a central component in the origin of physiological hand postural tremor. It is suggested that the different effect of mental calculation on hand postural and goal-directed tasks can be attributed to the different origins and characteristics of hand postural and goal-directed physiological tremor.

Time constraint and error corrections contribute to the increase of hand postural tremor during mental calculation

“…The onset, or the exacerbation of tremor during a mentally demanding task has already been regularly reported for pathological tremors [ [22] , [23] , [24] , [25] , [26] ], but, excluding our recent work [ 7 ], to our knowledge no other studies investigated the effects of mental performance on physiological tremor. Nevertheless, despite the aetiological differences, both pathological and physiological tremor are affected by stress [ 23 , 27 , 28 ], therefore, since the performance of a mental demanding task is considered a standard psychological stressor [ 9 , 29 , 30 ], it seems straight forward to attribute the increase in tremor to the increase in stress-induced sympathetic response, with related rise of circulating sympathetic hormones [ 22 ].…”

“…We have recently demonstrated that also postural physiological tremor is affected (increases) during a mental task [ 7 ]. However, since physiological tremor is not volitionally controllable [ 8 ], this result should be attributed to mechanisms other than cognitive-motor interference.…”

“…The mental task performed during the assessment of tremor in our previous work [ 7 ] involved arithmetic computations (continuously subtracting 13 from a 3-digit number), and the participant was required to provide the correct answer within 4 s. These methodological conditions are also commonly adopted as stressors in experimental settings to induce and study stress or anxiety in the participant [ 9 ]. Since stress is also known to stimulate the sympathetic nervous system [ 10 ] with related release of catecholamines, which could in turn increase muscle tremor [ [11] , [12] , [13] ], it could be suggested that the increase in tremor we observed during the metal task [ 7 ] was induced by an increase in stress with related release of catecholamines.…”

“…The primary aim of this research is therefore to determine whether the augmented physiological tremor during the postural contraction [ 7 ] should be attributed to the mental task per se or to augmented stress/anxiety levels induced by it. Secondary, we will try to understand whether voice vibrations also contribute to enhance tremor or not.…”

Effect of mental fatigue on hand force production capacities

“…Our result is consistent with a recent study, which did not reveal any effects of 100 min of cognitively demanding task on force steadiness during isometric pinch contractions [ 24 ], but also with another study performed on lower limb evidencing the maintenance of force steadiness during submaximal isometric knee extensions after 50 min of motor imagery [ 16 ]. A mental effort could impact force steadiness but only when mental fatigue is induced during muscle contractions with a concomitant cognitively demanding task [ 55 ]. The effects could be attributed to cognitivomotor interference [ 56 ] due to the simultaneous execution of two different tasks, as proposed by Budini et al [ 24 ].…”